Of the three major British party conferences, only that of the Liberal Democrats, which starts in Glasgow on Saturday, has serious claims to be democratic. They still use their conference to hammer out policy. Unlike the other two conferences, debates still take up the majority of the timetable. Only at Lib Dem conference is the language of motions, amendments, rulings from the chair, references back and summings-up still an integral part of proceedings. All of this may seem quaint, but healthy political parties ought to be democracies which debate their causes, not promotional machines for the leadership.

The Glasgow conference will certainly put some of this high-minded tradition to the test. Nick Clegg's leadership may not be under direct challenge – though the issue cannot be laughed off when his standing with the voters is so low. But Mr Clegg has to take his party seriously this week nevertheless. On at least four substantive issues – tax and the economy, tuition fees, Trident and nuclear power – this week's conference faces decisions which will help to define the party in 2015 . Meanwhile the choice of emergency motions, especially concerning the David Miranda arrest, are a litmus test of the modern party's civil liberties credentials.

Mr Clegg has decided to reply to the economic debate on Monday. He has taken this high-profile step because he is anxious that his party claims some political credit for the early signs of an economic recovery. But he must also therefore decide whether to stand out against amendments which draw a sharper dividing line between the Lib Dems and the Conservatives within the coalition than has previously been done. These amendments from social liberals call for rebalancing the economy, a focus on the most economically vulnerable, a boost for council house building and, after 2015, for fairer taxes on wealth and land. This is hardly Bolshevism. It would be extraordinary, not least in the light of Vince Cable's call for a boost to the minimum wage in the Guardian, if Mr Clegg did not accept them.

The party leadership should take a similarly relaxed view of the debate on tuition fees, where they face an amendment calling for a review in the next parliament of the current system of higher education finance. But the conference should back the intelligent and progressive policy put forward in this year's Lib Dem review of Trident, under which the UK would reduce the number of submarines as part of a multilateral approach to nuclear disarmament. In the most anguished debate of the week, however, the Lib Dems should be wary of abandoning their signature anti-nuclear power stance, a key issue for many of the party's depleted but committed core voters.

Liberal Democrat pride at proving themselves as a party of government inevitably jostles with anxiety about some of the compromises made, and the electoral damage sustained. The voters' verdict in 2015 may be brutal. One way of preventing that is to revive the party's reputation for standing up for civil liberties against the over-mighty state. The Lib Dems have a hugely important opportunity to burnish that reputation this week.

The Guardian's revelations about NSA and GCHQ internet data mining raise immense privacy and trust issues which must be properly debated not brushed indiscriminately under the carpet in the name of security. The main parties, as distinct from the Greens, who highlighted the issue on Friday, have not yet taken up their responsibility to do this. But Sarah Ludford's emergency motion no 6 on the arrest of David Miranda helps to open up the issues. It should be selected for debate in Sunday's ballot and supported on Wednesday if selected. British politics urgently needs a loud wake-up call about the state's threats to privacy. The Liberal Democrats need to give – and then act on – that call.